When I was still in college, co-conspirator Nick Rosenkranz published a justly famous article called “Federal Rules of Statutory Interpretation,” arguing that Congress could and should authorize written rules for interpreting federal statutes. (As Nick noted, there already are such rules in peripheral portions of the U.S. Code and in the states.)

That sounds fine to me and may even be a good idea. But in our paper, we argue that we should pay more attention to the laws we already have — unwritten though they are. The rules of statutory interpretation that Congress could pass would be law. So, too, the unwritten rules that we already have are law, in pretty much the same way.

Now the fact that the rules are unwritten can seem a little less intuitive, at first. But unwritten law is a deeply embedded part of our legal system. On the private law side we have unwritten law for interpreting contracts and wills. On the public law side we have unwritten law of criminal defenses (such as duress, necessity or self-defense in the federal system). Just the same, we have unwritten public law of interpretation — such as the rule of lenity or the canon against implied repeals.

Read more at The Washington Post